The use of inductance related measurements to monitor the movement of targets is known in the prior art. In US2014/0247040 by Reitsma et al, a position detecting system is taught which measures the increase/decrease in the power loss for a time varying field due to an increase/decrease in eddy currents as a conductive target moves closer/further from a coil, where the coil generates said time varying field. Or alternatively, the quality factor of a tank circuit is measured, where a coil which faces a conductive target provides the inductive reactance for said tank, and use is made of a negative impedance circuit. In US2014/0247090 by Reitsma resonant impedance sensing based on generation of a controlled negative impedance to monitor a target is taught.
Charge transfer based measurement techniques for capacitive sensing are well known in the prior art. Further, compensation for parasitic capacitances and slow environmental factor drifts are also known. Refer specifically to U.S. Pat. Nos. 8,395,395 and 8,659,306, which both share inventors with the present application.
Further, the prior art holds a fair number of alternative technologies and methods for capacitive sensing. Among these is capacitive sensing based on a measured change in the amplitude of an alternating voltage due to a change in a sensed capacitance, or sensing based on a measured change in the characteristics of a pulse or pulses due to a change in a sensed capacitance, or sensing based on a measured change in an oscillation frequency due to a change in a sensed capacitance, or sensing based on a measured change in a resonant frequency due to a change in a sensed capacitance.